Throughout most of history, there were no thermometers to measure temperature. This graph starts in the year -- at this point in time, Europeans weren't even using soap, Muslim philosophers were exploring astronomy and medicine, and the Chinese were inventing gunpowder.
Nobody was terribly concerned with measuring air temperature. So, how do we know how warm or cold it was back then??? Well, the first thing to notice is that the gray area, which represents uncertainty get it -- the gray area?
Although there are ways of estimating temperature, they are not as exact as modern technology. Secondly, what scientists have done is to go back and look at how fast things grew -- this is a proxy for temperature. It is not a perfect fit, and hence the large gray area. In order to do this, we need organisms that are long-lived and that show evidence of growth every year -- like trees.
Give it a try, using the sample tree trunk below:. Of course other factors are important as well. For example, a hot dry summer would probably result in little growth, and soil nutrients and pH would also affect growth. Clearly an entire temperature record based on one tree, or even trees worldwide, would be very shaky.
However, there are other long-lived organisms that we can use -- most importantly, coral. The heat reached all the way to the Antarctic, where the station at Esperanza Base, at the tip of the Antarctic Peninsula, appeared to set a new all-time record high temperature of Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling.
Based on NOAA's global analysis, the 10 warmest years on record have all occurred since , and 7 of the 10 have occurred just since Global Change Research Program. The amount of future warming Earth will experience depends on how much carbon dioxide and other greenhouse gases we emit in coming decades.
Today, our activities—burning fossil fuels and clearing forests—add about 11 billion metric tons of carbon to the atmosphere each year. According to the U. Climate Science Special Report , if yearly emissions continue to increase rapidly, as they have since , models project that by the end of this century, global temperature will be at least 5 degrees Fahrenheit warmer than the average, and possibly as much as If annual emissions increase more slowly and begin to decline significantly by , models project temperatures would still be at least 2.
Morice, J. Nicolas, and A. Qin, G. Plattner, M. Tignor, S. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. This is another point on which the datasets differ. The other three have grid boxes measuring five by five degrees. They also differ in how many land stations they have around the world, too. The four datasets differ in other important ways, too, including the time period they cover.
HadCrut4 stretches back the furthest to By combining the grid boxes, scientists work out average temperatures for the northern and southern hemispheres. How much each box contributes to the global temperature is adjusted to account for the fact that the degree of longitude is bigger at the equator than at the poles. Together, the hemispheric values provide an estimate of global average temperature.
To avoid the better sampled northern hemisphere from dominating the temperature record, scientists take the average of the two hemispheric values. Unlike the surface temperature record, tropospheric temperatures only extend back to the start of the satellite era in Lower troposphere temperature is different from that at the surface.
But scientists can use lower troposphere measurements as a further evidence of a changing climate. Several different groups now keep track of tropospheric temperatures and all four show a warming trend in the last 30 years. Intrigued, other scientists set about investigating and found errors in the original methods to do with differences between sensors on the satellites, and the satellites themselves drifting over time.
Once corrected, the differences between tropospheric and surface temperatures diminished — and a warming trend is now clear.
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